/*
 * This project provides a number of implementations for indexing and evaluating
 * <i>Continuous Top-k Queries over Text Streams</i>
 * and has been developped as part of the work described in the article:
 * 
 * Vouzoukidou, N., Amann, B., & Christophides, V. (2012, October). 
 * Processing continuous text queries featuring non-homogeneous scoring functions.
 * In Proceedings of the 21st ACM international conference on Information and 
 * knowledge management (pp. 1065-1074). ACM.
 * http://dl.acm.org/citation.cfm?id=2398404
 * 
 * This software is distributed under the GNU General Public License and as an
 * additional condition of usage, please cite the aforementioned article.
 * 
 * Copyright (C) 2012 ICS/FORTH, Greece and 
 *               2012 LIP6, France
 * 
 * Author: Vouzoukidou Nelly, email: nelly.vouzoukidou (at) gmail (dot) com
 * 
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program. If not, see <http://www.gnu.org/licenses/>.
 */
package gr.forth.ics.continuoustopk.utils;

import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 *
 * @author Vouzoukidou Nelly, email: nelly.vouzoukidou (at) gmail (dot) com
 */
public class MergedIterable<T> implements Iterable<T> {
    private Iterable<T> first;
    private Iterable<T> second;

    public MergedIterable(Iterable<T> first, Iterable<T> second) {
        this.first = first;
        this.second = second;
    }

    public Iterator<T> iterator() {
        return new Iterator<T>() {
            Iterator<T> terms = first.iterator();
            Iterator<T> secondIterator = second.iterator();

            {
                proceed();
            }

            public boolean hasNext() {
                return terms != null;
            }

            public T next() {
                if (!hasNext()) {
                    throw new NoSuchElementException();
                }
                try {
                    return terms.next();
                } finally {
                    proceed();
                }
            }

            private void proceed() {
                if (!terms.hasNext()) {
                    terms = secondIterator;
                    if (!terms.hasNext()) {
                        terms = null;
                    }
                }
            }

            public void remove() {
                throw new UnsupportedOperationException();
            }
        };
    }
}
